Process of making paper from a modified mercerized pulp



This invention is directed to a novel porous cellulosic web of improved physical properties which is suitable for impregnation with elastomers. This invention also relates to a novel method for preparing such cellulosic web and toa method for treating cellulosic fibers, especially regenerated cellulose such as viscose rayon, to impart improved physical properties thereto.

According to this invention, cellulosic fibers are curled and twisted by a chemical treatment which-comprises mercerizing a pulp suspension of cellulosic fibers, separating the mercerized pulp from the mercerizing solution in such manner to obtain a suspension containing approximately to 50% (preferably to by weight of the pulp, swelling the pulp, and acidifying the pulp suspension into a pH of 7 or less. This suspension can be formed directly into a web, or the treated pulp can be combined with approximately 5 to percent by weight of a second cellulosic pulp suspension of chemically untreated, highly beaten cellulosic fibers and formed into a web. This latter process produces a porous cellulosic web which comprises 5 to 30 weight percent of the untreated cellulosic fiber and 70 to 95 weight percent of the chemically treated cellulosic fiber. These novel cellulosic Webs possess very high wet and dry strength, both before-and after impregnation with an elastomer, a high degree-of porosity, and delamination resistance superior to that of prior art webs.

The mercerization of cellulose has long been known by the prior art. U.S. Patents 1,999,059, 2,008,142, and 2,083,575 are illustrative of such. Mercerization, as it is commonly understood, will make cellulose fibers more flexible. This is generally considered to be attributable to the fact that mercerization will reduce the overall crystallinity of the cellulose and also that the alkali solution will dissolve out the lignin and hemicellulose which tend to make the cellulosic fibers stiff and inflexible. 'Ihus, mercerization makes the fibers quite flexible; however, these fibers do not readily adhere together, thereby making it extremely diificult to fabricate them into a cellulosic web.

In the past, this problem has been overcome by the usage of resins and/ or synthetic fiber binders. Although this approach causes the fibers to adhere together, it greatly increases the expense of fabrication, since additional expensive equipment and materials must be used.

In addition to the problem mentioned above, the prior art has been unable to fabricate solid regenerated cellulose vfibers, such as viscose rayon, into coherent water-laid webs. These smooth, solid filaments have little tendency to bond to each other or to intertwine, thereby differing from hollow, fibers such as plant fibers. This renders the solid rayon fibers unsuitable for the preparation of waterlaid webs because of the low wet strength and because the dried webs are not coherent. This problem has been overcome by the chemical treatment of the fibers which is described in detail hereinafter. v

It is an object of this invention to provide a novel process for the treatment of cellulosic fibers to render them readily adhesive and easily fabricatable into cellulosic webs of improved physical properties. It is an additional object of this invention to provide a process for achieving such results without the usage of wet-strength agents, resins, or synthetic fiber binders. It is also an object of this invention to provide a process for producing such cellulosic webs. Other objects, features and advantages of this invention will be apparent to those skilled in United States Patent 0 3,332,833 Patented July 25, 1967 "ice v of the invention.

These and other objects are obtained by means of this invention which comprises a particular chemical treatment for cellulosic fibers and the usage of two different types of cellulosic fibers which interact to give the desired properties to the cellulosic web. The first cellulosic fiber is subjected to a chemical treatment which comprises mercerizing a suspension of such fibers, separating the mercerized pulp from the mercerizing solution to obtain a suspension containing approximately 10 to 50 weight percent of the pulp, swelling the pulp with either hot water or dilute acids, and acidifying the pulp suspension to a pH of 7 or less. This specially treated fiber can be formed into a cellulosic web of improved properties by any of the conventional procedures. The second type of cellulosic rubber, since the webs will have suflicient pore volume to allow uptake of at least their own weight of such impregnant. These cellulosic webs possess high wet-strength and dry strength both before and after impregnation and also have delamination resistance superior to that of cellulosic webs of the priora rt.

The explanation for this improvement in the physical properties of the cellulosic web is not clearly known. 35

However, it is clear that the cellulosic fibers which have been chemically treated are twisted and curled. As a result, these fibers will not lie flat when pressed into a web. Instead, it is believed that these fibers become tangled and inter-woven, thereby forming a porous cellulosic web of improved delamination resistance, increased porosity, and high wet and dry strength.

Mercerization per se does not form a part of this invention. Thus, in general, any conditions, i.e., time, temperature and materials, known by the prior art are suitable for usage in this invention. Conditions which have been found to be especially suitable are an aqueous solution of sodium hydroxideof from 2 to 20 weight percent concentration and a temperature of from 0 to 50 C. It is preferable that the mercerization be instantaneous, but it can be conducted for a longer period of time if desired. It has also been found to be advantageous to the mercerization process if the cellulosic fibers are beaten very thoroughly in a suitable apparatus prior to mercerization.

When the merceri'zed pulp is separated from the mercerizing solution, the pulp retains a considerable amount of the mercerizing solution. In order to remove undesirable impurities, such as lignin which is dissolved in the alkaline liquor, it is advantageous that the pulp be as dry as possible. However, the pulp cannot be permitted to become completely dry as the mercerizing solution (sodium hydroxidefwhich has been absorbed into the pulp will tend to carbonate such. To preclude this carbonation, the

to 25% by weight of the pulp. The separation of the pulp from the mercerizing solution is by mechanical separation, such as centrifugation, filtration, or by running on a paper machine.

The swelling of the cellulosic fibers is performed by adding the suspension of pulp in the mercerizing solution to a stirred vessel containing hot water or a suitable dilute, water soluble acid, such as acetic acid. When water is the swelling medium, the temperature may be from '60 to 100 C., preferably 90 to 100 C., and the treatment time can range from 5 minutes to 1 hour. If the swelling medium is a dilute acid, the temperature should be in the range of from to 40 C. The treatment time should again be in the range of from minutes to 1 hour. The concentration of the dilute acid should be in the range of from about 1 to 40 weight percent since a more concentrated acid will produce hydrolysis of the cellulose. It is to be understood that any dilute, water soluble acid may be used as the swelling medium. Examples of such acids are: oxalic, sulfuric, hydrochloric, nitric, acetic, etc.

The acidification of the swelled fibers may be done by usage of any of the dilute, water soluble acids mentioned above. The concentration, temperature, and treatment time are also the same as those used in the swelling step.

If the swelling is achieved by usage of a dilute acid, the pulp suspension will also be acidified at the same time by this acid. It is only when the pulp is swelled by the hot water that the suspension has to be subsequently acidified by the dilute acid in the manner described.

The pulp suspension must be acidic in nature if the resulting web is to have the improved physical properties. If the suspension is not acidic, the fibers will be hard and stiff. The dilute acid will remove the remaining traces of the sodium salts present in the suspension and make the (fibers soft and flexible. As shown by the results of the working examples, cellulosic webs made from fibers treated in this manner have a delamination resistance of approximately two times that of the prior art.

If desired, the acidified cellulosic fibers can be subjected to a chemical treatment to insure that the fibers do not bond to each other as they dry. Such treatment comprises separating the cellulosic fibers from the acidifying solution by centrifugation or other mechanical separation to make them as dry as possible, i.e., the percent of acidifying solution retained by the fibers will be as low as possible. The cellulosic fibers will then be immersed in a vessel containing a solvent which is capable of extracting water from the fibers. Examples of such solvents are acetic acid, glacial acetic acid, acetone, methyl alcohol, methyl ethyl ketone, ethyl alcohol, and propyl alcohol. The time required for this treatment should be in the range of from 1 to 60 minutes. The temperature can be in the range of from to 40 degrees C.

In general, any known cellulose fiber may be used as the fiber to be subjected to the chemical treatment described above. In regard to the untreated cellulose fiber, any known cellulose fiber may be used. Illustrative examples are wood pulp, cotton, hemp, regenerated cellulose (rayon), and bamboo.

It is essential to the success of this invention that the chemically untreated fibers be highly beaten before combining such with the chemically treated fibers. The fibers may be thoroughly beaten in any of the commercial devices such asa ball mill, Jordon or Hollander mill or in laboratory apparatus such as a Waring Blendor. The length of beating, will vary depending upon the efficiency of the mixing apparatus. In general, this time will be in the range of from about /2 to 2 hours, with the primary requirement being the fibers are beaten until they possess a Canadian Standard Freeness of 300 or less.

The impregnation procedure and impregnating agents do not form a specific part of this invention. Any conventional impregnation procedure, such as mentioned in US. Patent No. 2,697,048 may be used. Convention-a1 impregnating agents, such as styrene-butadiene rubber, acrylic rubbers, polyvinyl chloride latexes, polymethane, and the like are suitable for usage in this invention.

The following examples are used in the illustration of this invention, but are not to be considered as limiting the scope of this invention.

Example I 625 grams of pulp consisting of 120 grams of unbeaten kr-aft softwood pulp and 505 grams of water was stirred into a solution of 240 grams of sodium hydroxide in 480 milliliters of water at ambient temperature. This mixture was stirred until all fibers were thoroughly wet and the mixture was homogeneous. The suspension was then filtered with suction on a wire screen in a Biichner funnel. The pulp was then centrifuged for five minutes to remove additional sodium hydroxide solution therefrom. The pulp fibers comprised approximately 25% by weight of the resulting mass. The alkali pulp was next added to one gallon of 1% (concentration by weight percent) aqueous sulfuric acid at ambient temperature and stirred with a mechanical stirrer for ten minutes. A litmus paper test indicated that the suspension was acidic, i.e., the pH was less than 7. The swollen fibers were collected by filtration and washed four times with two-liter portions of water. Ten grams (dry basis) of this pulp was then dried in a centrifuge, soaked in 200 ml. of glacial acetic acid (99.8% purity) for ten minutes, and then dried thoroughly.

Ten grams of untreated kraft softwood fibers were beaten with 600 ml. of water for one hour in a Waring Blendor. Thirty milliliters of the resulting suspension (0.5 gram solid) was dispersed in water in a paper sheet mold. Six grams of the chemically treated pulp prepared above was dispersed by beating ten seconds in a Waring Blendor with 600 ml. of water. This was then mixed with the beaten pulp in the sheet mold and formed into a web.

The resulting web, after drying, had a total pore volume of 1.79 cubic centimeters per gram, whereas a similar web made from untreated fibers had a pore volume of only 0.96 cubic centimeter per gram. After impregnation with styrene butadiene rubber latex, the web had a delamination resistance of 4.00 pounds per inch, whereas that made from untreated fibers impregnated with an equal amount of the same rubber had a delamination resistance of only 1.47 pounds per inch.

Example 11 The procedure of Example I was followed, except that the first cellulosic pulp was beaten for thirty minutes in a Waring Blendor before it was treated with sodium hydroxide. The product had a pore volume of 1.26 cc./g. and a delamination resistance of 4.00 lb./ in. The control had a pore volume of 0.96 cc./g. and a delamination resistance of 1.52 lb./in.

Example III The procedure of Example I was followed, except that the alkali pulp was added to one gallon of water at 95 C., instead of sulfuric acid solution. After the hot water treatment, the swollen fibers were redispersed in water and acidified to pH 4 with glacial acetic acid. The product had a delamination resistance of 2.72 lb./ in. while that of the control was 1.50 lb./in.

Example IV The procedure of Example I was again followed, except that the second cellulosic fiber was made from Manilla hemp fibers which had been beaten for minutes. Four sheets were made using various amounts of beaten hemp. The experimental results of this example are summarized in the table:

Ml. hemp Grams hemp Resulting pore Delamination slurry used (dry basis) volume (cc./g.) resistance, 1b./in.

impregnation with a comparable amount of rubber.

Example V A suspension of 120 g. of viscose rayon acetate monofilament, chopped to of an inch in length, in 500 m1. of water was stirred into' a solution of 240 g. of sodium hydroxide in 480 ml. of water at ambient temperature. As' soon as all fibers were wet and the mixture was homogeneous; the suspension was filtered with suction on a wire screen in a Biichner funnel. The fibers were pressed as dry as possible in five minutes, then added at once to one gallon of water at 95 C. and stirred with a mechanical stirrer for ten minutes. The swollen fibers were collected by filtration and washed four times with twoliter portions of water. They were redispersed in water and acidified to pH 6 with glacial acetic acid.

Six grams of the treated pulp (dry basis) was beaten ten seconds in a Waring Blendor with 500 ml. of water and formed into a handsheet in a paper sheet mold. The wet web was initially 203 mm. in diameter, but shrank to 173 mm. as it dried. The resulting dry web was strong and flexible, although bulky and porous. Individual fibers pulled from the web were curled and looped. Microscopic examination of the web showed a high degree of fiber entanglement. A similar web made from untreated rayon fibers shrank only to a diameter of 197 mm. (3.0% shrinkage as compared to 14.8% in the treated web) and was so weak that it could not be moved without support. The individual fibers in the untreated web were essentially straight, and did not appear to be intertwined in the web.

Cellulosic webs made by the processes herein described are suitable for numerous uses. For example, they have application in any of the known paper-making processes, as well as processes for producing artificial leather, tape backing, bookbinding materials, and gaskets. In addition, these webs are applicable to certain upholstering uses, e.g., door paneling stock.

It is to be understood that many equivalent modifications will be apparent to those skilled in the art from the reading of the foregoing disclosure without a departure from the intended concept of the invention.

I claim:

1. A process or treating a cellulosic fiber which comprises:

(a) mercerizing a pulp suspension of cellulosic fibers;

(b) separating the mercerized pulp from the mercerizing solution to obtain a suspension containing approximately 10 to 50% by weight of the pulp;

(c) treating the pulp for 5 minutes to 1 hour with water at 60-100 C. to further swell the pulp;

(d) then acidifying the pulp suspension to a pH not greater than 7; and

(e) forming the pulp into a web.

2.. The process of claim 1 in which the suspension contains approximately to by weight of the pulp when separated from the mercerizing solution.

3. A process for treating a cellulosic fiber which comprises:

(a) mercerizing a pulp suspension of cellulosic fibers;

(b) separating the mercerized pulp from the mercerizing solution to obtain a suspension containing approximately 20 to 25% by Weight of the pulp;

(c) treating the pulp for 5 minutes to 1 hour with water at 95 C. to further swell the pulp;

(d) acidifying the pulp suspension to a pH not greater than 7; and

(e) forming the pulp into a web.

4. The process ofclaim 2, wherein, following the step of treating the pulp to further swell same, the pulp is treated with dilute sulfuric acid of approximately 1 weight percent concentration.

5. The process of claim 2 wherein the acidified pulp is washed with a solvent selected from the group consisting of glacial acetic acid, acetone, methyl alcohol, methyl ethyl ketone, ethyl alcohol, and propyl alcohol to extract water from the fibers prior to forming the pulp into a web.

6. The process of claim 1 in which the cellulosic fiber is viscose rayon.

7. A process for providing a porous cellulosic web of improved physical properties which comprises:

(a) mercerizing a first pulp suspension of cellulosic (b) separating the mercerized pulp from the mercerizing solution to obtain a suspension containing approximately 10 to 50% by weight of the pulp;

(c) treating the pulp for 5 minutes to 1 hour with water at 60-l00 C. to further swell the pulp;

(d) then acidifying the pulp suspension to a pH not greater than 7;

(e) subsequently combining said acidified pulp with approximately 5 to 30% by weight of a second cellulosic pulp suspension of chemically untreated, highly beaten cellulosic fibers; and

(f) forming said combined pulp into a web.

8. The process of claim 7 in which the first pulp suspension contains approximately 20 to 25 by weight of the pulp when separated from the mercerizing solution.

9. A process for providing a porous cellulosic web of improved physical properties which comprises:

(a) mercerizing a first pulp suspension of cellulosic (b) separating the mercerized pulp from the mercerizing solution to obtain a suspension containing approximately 20 to 25 by weight of the pulp;

(c) treating the pulp for 5 minutes to 1 hour with water at C. to further swell the pulp;

(d) acidifying the pulp suspension to a pH not greater than 7;

(e) subsequently combining said acidified pulp with approximately 5 to 30% by weight of a second cellulosic pulp suspension of chemically untreated, highly beaten cellulosic fibers; and

(f) forming said combined pulp into a web.

10. The process of claim 8 in which, following the step of treating the pulp to further swell same, the pulp is treated with dilute sulfuric acid of approximately 1 weight percent concentration.

11. The process of claim 8 wherein the acidified pulp is subsequently washed with a solvent selected fromthe group consisting of glacial acetic acid, acetone, methyl alcohol, methyl ethyl ketone, ethyl alcohol, and propyl alcohol to extract water from the fibers prior to combining such with said second cellulosic pulp suspension.

12. The process of claim 11 wherein the solvent is glacial acetic acid.

13. A porous cellulosic web which comprises 5 to 30 Weight percent of chemically untreated highly beaten cellulosic fiber and 70 to 95 weight percent of a cellulosic fiber prepared by the method of claim 7.

14. A porous regenerated cellulosic web which comprises iregenerated cellulosic fibers prepared by the method of claim 7.

15. The web of claim 14 in which the regenerated cellulosic fibers are viscose rayon.

References Cited UNITED STATES PATENTS 1,857,100 5/1932 McCormick 8-125 2,015,132 9/1935 Young 162-157 2,083,575 6/1937 Novak 162-157 2,528,793 11/1950 Secrist 8-125 DONALL H. SYLVESTER, Primary Examiner.

HOWARD R. CAINE, Examiner. 

1. A PROCESS OR TREATING A CELLULOSIC FIBER WHICH COMPRISES: (A) MERCERIZING A PULP SUSPENSION OF CELLULOSIC FIBERS; (B) SEPARATING THE MERCERIZED PULP FROM THE MERCERIZING SOLUTION TO OBTAIN A SUSPENSION CONTAINING APPROXIMATELY 10 TO 50% BY WEIGHT OF THE PULP; (C) TREATING THE PULP FOR 5 MINUTES TO 1 HOUR WITH WATER AT 60-100*C. TO FURTHER SWELL THE PULP; (D) THEN ACIDIFYING THE PULP SUSPENSION TO A PH NOT GREATER THAN 7; AND (E) FORMING THE PULP INTO A WEB. 